1. Field of the Invention
The present invention relates to the field of modems, i.e., modulator/demodulator sets for the transmission and reception of digital data over phone lines.
2. Prior Art
Various techniques are well-known and widely used for digital communication over phone lines using modems, i.e., modulator/demodulator sets at each end of the phone line. Applications for such equipment include communication between remote, even portable terminals and a central computer, and communications between computers. With the recent advances in microprocessor and other digital integrated circuit technology which has greatly increased computer capability and reduced cost in the burgeoning personal computer market, there is a corresponding expanding market for competitively priced modems capable of communicating between themselves or communicating with pre-existing modems of pre-established characteristics. Because of the number of different pre-existing modems, each with their own communication characteristics, prior art modems are generally each specifically identified as to type, and each is generally limited to communication with another modem of the same type.
In the prior art, modems were generally built using discrete components and standard integrated circuits in a special circuit design to achieve the desired modem type compatability. Attempts have been made to provide specialized integrated circuits to achieve lower cost modems, although certain unique requirements of modems have limited the success of such integrated circuit devices. In particular, considerable filtering is required in the receiver as part of the signal detection. Heretofore, this filtering, which comprises a substantial portion of the receiver itself, has not been done on chip, with the result that a number of circuit functions accomplished by the special integrated circuits is limited and the total parts count required to achieve an operative modem using the integrated circuits is still quite substantial.